How does the drape and compressibility of XP compare to 3D ?  (Same, 20% better, etc).

Also, is there a way to quilt XP without making big yarn-sized holes in the cover & liner ?

Thanks.

XP is a little less bulky than 3D was.  Drape seems about the same.  I haven’t seen any quantitative percentages on these qualities.

You can use seam stabilization techniques if you want to avoid yarn loops.  Or, don’t use any interior quilting and deal with the durability issues.  Or, only use yarn loops between the liner and insulation and deal with the floating shell.

Seam stabilization is a technique used with synthetics whereby corresponding seams on the shell and liner are joined either by sewing the seam allowances together or by using fabric to join them similar to a baffle. 

Yarn loops are chumpy looking but are easy, effective, and recommended.

I would like to make something that looks more professional, is durable enough for washing in a front-loading machine, and doesn’t have the water entry holes of yarn loops.  I have a standard sowing machine (Bernina 1008).

My Sierra Designs 3-D filled sleeping bag appears to through stitched when you look at the shell or liner.  But when you examine it in detail, it turns out the stitching just goes part of the way through the insulation since the stitching on the shell and liner is separated by about 3/4”.  It’s a “Wild Bill” model bag, that retailed for around $160, so it would suprise me a lot if they used baffles (assuming 3-D came in a sheet like XP).  Initially, I thought they used 2 layers of thin insulation, through stitched one to each of the shell and liner, and then joined the two at the side seams.  But I can’t make the two inner layers seperate even a little bit, so this must not be how it was done.  Do you have any idea how this can be done using a standard home sowing machine ? 

If not, the seam stabilization techniques seems like the best alternative - but I can’t find any references on how to do it using a Google search.  Is it suitable for large panel items like quilts and sleeping bags ?  Can you give more details on how it’s done ?

Your wild bill bag most likely uses seam stabilization where panels are joined, and offset quilting or shingling on the interior of the panels.

A few careful minutes with a seam ripper and access to the inside of your bag (or any other synthetic bag) will make things crystal clear.